Because the diagnosis of high blood pressure depends on blood pressure readings, it's essential that blood pressure be measured carefully. Avoid strenuous exercise, smoking, eating, and drinking caffeinated beverages (coffee, tea, colas) for at least one hour before you have your blood pressure taken. You should be seated for at least five minutes before the reading is taken, and you should not talk while your blood pressure is being measured. Two readings should be recorded and averaged. If your blood pressure is high, your doctor should examine your eyes, heart and nervous system (to look for brain damage). If your examination does not show evidence of long-standing hypertension, your doctor will have you return to the office at least two more times to have your blood pressure checked before diagnosing you with hypertension. A single high reading can happen to anyone.
Once you are diagnosed with hypertension, other tests will be done to see if the high blood pressure has caused organ damage. These test can include blood tests to check kidney function, and an electrocardiogram (EKG) to look for thickening of the heart muscle, reduced blood flow to your heart or irregular heart rhythms.
Prehypertension, readings above 120/80 but less than 140/90 on three separate occasions, is not a disease. It means you are at higher than average risk for developing hypertension.